This invention relates to injection laser manufacture and in particular to the manufacture of an (In,Ga)(As,P) laser having the structure referred to sometimes as an Inverted Rib Waveguide (IRW) laser, and also referred to as a Plano-Convex Waveguide (PCW) laser.
An IRW laser is characterized by having, between the active layer and the substrate, an intermediate layer which provides a measure of dielectric waveguiding effect in the lateral direction by virtue of a rib formed in its surface facing the substrate, this rib extending into a material of lower refractive index. In the case of (In,Ga)(As,P) lasers grown upon InP substrates, the low refractive index of InP relative to that of (In,Ga)(AsP) makes it possible to adopt a relatively simple structure in which the intermediate layer is grown directly onto the surface of the substrate so that its rib extends into the substrate material.
The manufacture of (In,Ga)(As,P) IRW lasers has been described by M. Ueno et al in IEEE Journal of Quantum Electronics, Vol. QE-17, No. 9, pp. 1930-40 (September 1981), by K. Sakai et al in the same Journal, Vol. QE-17, No. 7, pp. 1245-50 (July, 1981), and by Y. Noda et al in Electronics Letters, Vol. 17, No. 6, pp. 226-7 (March 1981). However, the approaches described in these articles have certain disadvantages which will be discussed in some detail later and which are overcome by the present invention.